Renewable oils, which include vegetable and animal oils, are well known for their nutritive and cooking value. Increasingly, they are also becoming an alternative fuel source for transportation and manufacturing. Because renewable oils are generally produced though biological processes that directly or indirectly remove carbon from the atmosphere, they are considered carbon neutral. In contrast, fuels derived from non-renewable sources like coal and petroleum add carbon dioxide and other pollutants to the atmosphere without a corresponding removal step. Heightened concerns about global warming and other environmental problems have spurred interest in replacing non-renewable fuels with ones derived from renewable sources such as renewable oils.
Renewable oils are typically extracted from their natural sources in an unrefined form that is sometimes referred to as crude oil. These crude oils include a variety of impurities, such as gums, waxes, phosphatides, sterols, and free fatty acids, among other impurities. For most applications, at least a portion of these impurities have to be removed or converted into something else before the renewable oil can be used. For example, crude vegetable oils are typically degummed, dewaxed, bleached, and deodorized before being used as a food ingredient or for cooking.
In many processes where renewable oils are used to make transportation fuels, reducing the levels of free fatty acids and other impurities in the crude oil is important. For example, the process of converting renewable oils into biodiesel fuel involves the reaction of triglycerides with alcohols to produce fatty esters. In many biodiesel processes the presence of even small quantities of free fatty acids produced by the degradation of the triglycerides can create significant reductions in the yield of biodiesel.
Unfortunately, conventional processes for removing free fatty acids and other impurities from crude renewable oil often remove significant quantities of triglycerides and other desired components, as well as create a large stream of waste products. For example, conventional methods for removing free fatty acids often involve mixing the crude oil with several rounds of aqueous solutions of acid and/or base. The multiple washings extract a significant quantity of the oil with the free fatty acids, and also create a large waste stream. Subsequent pH adjustments consume additional process chemicals and create even more waste. Moreover, the separation of the waste stream from the purified oil by, for example, centrifugation, distillation, filtration, etc., requires significant expenditures of energy that decrease the net energy yield in the final fuel product. Thus, there is a need for improved purification processes for renewable oils that reduce the materials and energy expended by the process. This and other challenges are addressed in the present application.